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RISS 인기검색어
- 검색키워드
- 저자 : Mustaqima, Millaty (검색결과 1 건)
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(The) resistance switching properties in sol-gel derived cobalt ferrite (CoFe2O4) thin films
Mustaqima, Millaty Hankuk University of Foreign Studies Graduate Scho 2015 국내석사
The Resistance Switching Properties in Sol-Gel Derived Cobalt Ferrite (CoFe2O4) Thin Films Recently, ferrimagnetic ferrite materials have been exploited as resistance switching materials owing to their insulating electrical properties. Cobalt ferrite (CoFe2O4), one well-known spinel ferrite, has been investigated for its application in magneto-optics and magneto-electric devices due to its rich and unique magnetic and electric properties. In cobalt ferrite, coupling between resistance switching and magnetic properties may be obtained in one material. Resistance switching (RS) phenomena is defined as a repeatable switching between a high resistance state (HRS) and a low resistance state (LRS) by applying either a voltage or current stimulation. Resistance switching random access memory (RRAM) based on the RS behavior is one of the most promising candidates for the next non-volatile memory. However, most RRAM devices show a wide variation in the high-to-low resistance switching voltage (VSET) which hinders them from the practical application. Overcoming this obstacle has become a focused issue in the resistance switching studies. In this work we prepared the cobalt ferrite thin films by the sol-gel method under different conditions and investigated their RS properties to propose a feasible approach to stabilize the set voltage. Textured polycrystalline CoFe2O4 thin films were deposited on Pt(111)/TiO2/SiO2/Si substrates through a sol-gel method. We varied the thickness of the films by using precursor solutions with different concentrations of 0.1, 0.2, and 0.3 M, and by depositing 5, 8, or 10 layers on the substrate by spin-coating. X-ray diffraction spectra indicated that the spin-coated films were preferentially oriented in the direction when the precursor concentration of the solution was higher than 0.1 M. The surface morphology inspected by scanning electron microscopy revealed that CoFe2O4 thin films prepared with 0.2 M solution and 5 time spin-coatings had a smoother surface as compared with other conditions. The average thickness of each coating was about 50 nm. The magnetic properties measured using vibrating sample magnetometer showed magnetic anisotropy as evidenced from the difference in the in-plane and out-of plane hysteresis loops, which was attributed to the textured orientation of the CoFe2O4 thin films. Pt/CoFe2O4/Pt structures were prepared to investigate the resistance switching behaviors. The post-annealing conditions and film thickness were varied for CoFe2O4 thin films. Our results showed that resistance switching without a forming process is preferred to obtain less fluctuation in the set voltage, which can be regulated directly from the preparation conditions of the CoFe2O4 thin films. Therefore, instead of thicker film, CoFe2O4 thin films deposited by two times spin-coating with a thickness about 100 nm gave stable resistance switching with the most stable set voltage. Since the forming process and the large variation in set voltage have been considered as serious obstacles for the practical application of resistance switching for non-volatile memory devices, our results could provide meaningful insights in improving the performance of ferrite material-based resistance switching memory devices.
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